In a mobile communication system, a basic principle of adaptive coding and modulation is to select an appropriate modulation and coding scheme based on change in a wireless channel. A receiving end may perform channel measurement to obtain Channel State Information (CSI) and feed the CSI back to a sending end. The sending end may perform scheduling based on system resources and the CSI fed back by the receiving end, select a most appropriate downlink modulation and coding scheme, and optimize a system throughput.
In some application scenarios, the CSI feedback in a related technology may be limited. For example, at a Long Term Evolution (LTE) Release-13 stage, in order to save transmitting power and to provide coverage for enhanced Machine Type Communication (MTC), a User Equipment (UE) may not support measurement and feedback of periodic CSI, so that the sending end cannot obtain the CSI. In fact, a new CSI feedback solution may be taken into consideration to assist the sending end in adaptive coding and modulation.
At an LTE Release-12 stage, Device to Device (D2D) may support broadcast communication only, and the receiving end may not perform CSI feedback. Unicast D2D may improve the system performance, and introduction of CSI feedback may improve gains of the unicast D2D. A soft Hybrid Automatic Repeat Request (HARQ) may serve as a potential CSI feedback solution for the unicast D2D.
The essence of the soft HARQ is an implementation manner of CSI feedback. In the HARQ of a related technology, when a data packet is correctly received, the receiving end may respond with Acknowledgment (ACK), and otherwise, the receiving end may respond with Negative Acknowledgment (NACK). When this technique is adopted, the sending end cannot obtain more link information from the responses. In the soft HARQ, by increasing a small amount of feedback bits, other information may also be attached when the receiving end sends the ACK/NACK, and the attached information may be used to indicate various link information, such as posterior CSI, a difference between a current Signal to Interference and Noise Ratio (SINR) and a target SINR, an error pattern of a received code block, an error bit rate, a coding rate, a modulation scheme, and time-frequency resources occupied by data. The attached information may assist the sending end in adaptive adjustment of a transmission parameter, so that HARQ transmission may be better implemented. To sum up, the soft HARQ can implement link adaption under limited signaling overhead and implementation complexity. Meanwhile, compared with the traditional CSI feedback, the soft HARQ can perform CSI feedback more quickly and more immediately.
In a soft HARQ technology, the feedback bits may indicate other link information (such as transmission parameter) in addition to ACK/NACK. However, there is no specific solution for determining the link information. Therefore, a new technology may be needed to determine the link information. The link information assists the sending end in better HARQ transmission. Under the situation of a non-soft HARQ, if the link information is determined in an appointment manner, the sending end and the receiving end may acquire the link information simultaneously without signaling interaction, and in this case, the receiving end may not perform link information feedback.
Any effective solution has not been proposed yet for a problem in a related technology regarding how to determine a transmission parameter.